Barrel Twist and ammo selection

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So I got rid of my 1-9 twist barrel and am installing an upper with a 1-7 twist barrel. Thing is, I have a bunch of m193 and other 55gr ammo saved up that Im worried wont shoot well out of my new barrel. Are my worries unfounded? Or should I be getting rid of my 55gr ammo and buying heavier stuff. Obviously from now on Ill be buying 62gr and heavier ammo, unless there arent any issues with shooting 55gr ammo in a 1-7 twist barrel...

Nevermind, found my answer over on m4carbine.net. Apparently a 1-7 twist is fine for bullets as light as 40gr (it is a bullet's length that matters, not necessarily weight), and a bullet being "overstabilized" is a myth for all intents and purposes.

A 1:7 will group OK with 55-gr M193. Might not give it a benchrest group, but for practical purposes, it'd be fine. Though I've seen some sweet handload Nosler Ballistic Tip loads that went through a lot of different rifles with all sorts of rifling twists just fine too.

I've been shooting 1:7 twist Colts since the mid 80s with both 55grn and 62grn bullets.
I have seen no appriciable difference in accuracy. What does effect the bullet is distance, wind and barrel lenght.

So I got rid of my 1-9 twist barrel and am installing an upper with a 1-7 twist barrel. Thing is, I have a bunch of m193 and other 55gr ammo saved up that Im worried wont shoot well out of my new barrel. Are my worries unfounded? Or should I be getting rid of my 55gr ammo and buying heavier stuff. Obviously from now on Ill be buying 62gr and heavier ammo, unless there arent any issues with shooting 55gr ammo in a 1-7 twist barrel...

Any help would be most appreciated! Thanks!

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Did you try heavier bullets in your 1/9 barrel before you changed it for a 1/7 barrel?

I shoot Hornady Superformance 75 grain ammunition in my 1/9 barrel without any problems. With a scope, they are tight groups. With Iron Sights, not as much as I want. But that is on me, not the rifle twist.

At 50 yards, I doubt it'll make a difference. I've shot 1" groups at 50 with my Aimpoint, using XM193, XM855 and 5.56 TAP 75grn back to back, with relatively minimal shift in POI.

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Yeah, I didn&#8217;t word my post correctly.:embarassed: What I meant to ask BB is if he has shot that gun with heavier bullets at longer distances and what groups he got then.
As a comparison to the xm193.

Nevermind, found my answer over on m4carbine.net. Apparently a 1-7 twist is fine for bullets as light as 40gr (it is a bullet's length that matters, not necessarily weight), and a bullet being "overstabilized" is a myth for all intents and purposes.

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Bullet overstabilization is not a myth. It is a very real occurance with lighter, shorter bullets at high velocities from fast twist barrels. It simply is not a factor with 5.56 projectiles from a 1/7 twist barrels inside of 300 yards. Stretch those 40 gr bullets out to 500 yards and the bullet will no longer be pointing in the direction of travel. It will be pointing in the direction of departure because, being overstabilized it cannot turn downward, or they will turn downward at varying points in the flight path causing more vertical dispersion than heavier bullets.

arushus
I guess it really depends on what your uses are. If your just plinking /trianing to shoot at short ranges 0-100 yards then you'll not see the difference of using light bullets. I don't only use my AR's for HD/SD they hunt as well so I need accuracy out to 400 yards. My 1:7' twist give me minute of man accuracy out 300 yards with 55gr FMJ probably further but my eyes are not twenty anymore. So that's my personnal limit especially with irons. Scoped I can still get out there. But normally when I know longer then 200 yards shots will be the norm I go up in bullet wt 69gr or more.

I disagree with that chart. I don't think a 1:9 twist can shoot a 62gr bullet any more accurately than a 1:7 twist. Besides, it's not the weight, it's the bullet length. Hornady's 75gr bullets supposedly shoot just fine in 1:9 twists. That's the claim anyway. I realize we have to generalize to weight but that chart is overly restrictive, IMO.

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